The present invention relates to the field of signal coupling, receiving, and driving techniques, and more particularly to transmitting timing, triggering, front-stage-driving, and last stage driving signals used for driving MOSFETs (Metal Oxide Silicon Field Effect Transistor) where high voltage isolation between the signal source and the MOSFETs is needed.
Conventional devices used for coupling signals in high voltage isolation applications include optical couplers and transformers. An optical coupler includes a light emitter and receiver. The former converts electric signals into light signals and the latter converts the light signals back to electric signals. In this manner the coupling function is completed.
A transformer device converts an electric signal into a magnetic signal by sending a voltage to a first coil winding, conventionally called the primary winding. The magnetic field is then picked up by a second coil winding, conventionally called the secondary winding, and converted back into an electric signal, which is similar to the original signal sent to the primary winding.
The optical coupler can provide high voltage isolation because the light can travel across a free space, such as air, or an optically transparent but electrically isolative material, such as clear plastic and glass. However the optical coupler can only couple signals having a low power level, such as a few milliwatts. When high power signal coupling is needed, the optical coupler becomes very expensive and high cost lasers have to be used as the emitter and high cost large area photo-detectors have to be used as the receiver for sending and receiving the high power signals respectively.
The transformer device can provide high power coupling, or high power transmission, with high voltage isolation capability. However both the cost and size of the transformer device increase dramatically as the power increases. Furthermore, when low frequency signals need to be coupled, or transmitted, the transformer device size increases compared with that required for transmitting a same power signal having a higher frequency. Keeping the size of the transformer device constant, the level of power that can be transmitted is lower for signals of low frequencies and the efficiency lower.
There is therefore a need in the art for a low cost high voltage isolation device capable of transmitting pulse signals having a wide range of pulse widths with a short time delay and precise timing.